This invention relates to the field of transportation, and more particularly to means for the protection of lading being transported in vehicles from damage resulting from shifting of the lading due to impacts and oscillations of transportation.
In the course of loading cargo into transportation vehicles for carriage, voids inevitably develop as a result of the relations between dimensions of cargo elements and the dimensions of the vehicles themselves. If compensation is not made for these voids after loading is completed, by dunnage appropriate to hold the lading in place approximately as loaded, the lading during subsequent movement of the vehicle in transit will move within and in relation to the vehicle. Damage of the vehicle by the lading, and of the lading by the vehicle, as well as mutual damage by lading elements, is the result.
No matter how tightly a given lading is loaded in a given vehicle, small spaces are incrementally distributed longitudinally, laterally, and vertically throughout the load, which have a tendency, under the dynamic forces present during transit, to close up as the load "tightens" and "shakes down". For example, the inside length of a railroad boxcar may be 50 feet, 6 inches, while the actual accumulated length of the lading may be 48 feet, consisting of 12 four foot long units: in practice the length of such a load can seldom be made closer than 48 feet 6 inches. This leaves a two foot initial void space which must be filled if the lading elements are to be prevented from shifting with consequent damage.
Some sort of separator, box, strap, or dunnage is required to fill this void. If a fixed separator two feet long is inserted in the void before transit, which is a common practice, the load may tighten up in transit so that there is as much as 6 inches of additional void created, which permits the lading elements to slide and slam into each other, the separators, and the vehicle, frequently damaging some or all of these.
The "floating" concept of lading has been proposed to overcome this. According to this concept, the lading is positioned in the vehicle spaced from the vehicle walls by more than the mean distance the load can be expected to shift in each direction during transit. Movements of the lading are converted to sliding friction between the lading and the car floor. This is a rather uncertain lading protection arrangement, and makes rather inefficient use of the floor area of the car.
Dynamic devices have also been proposed such as expanding mechanical panels linked by mechanically loaded connectors, inflatable paper or rubber bags, used alone or incorporated between two panels, and various belt or strap devices attached to the car which suspend the lading in such a way as to transfer peak force loadings away from the lading. Semi-permanent accessories such as load dividers, bars, air expanded panels, and bolt attachments to transport vehicles have the disadvantage of being expensive and subject to loss, damage, and vandalism, thus requiring replacement. On the other hand, disposable accessories raise a serious problem at locations where a great quantity of goods is regularly received, and physical disposal of "disposable" accessories must be accomplished by haulage to a remote dumping area.